[Foucault-L] source of quote

I seem to remember Foucault writing something along the following lines:

"Men generally know what they are doing, and frequently know why they are
doing it. But what they do not so often know is what what they are doing
does."

This is my wording, not Foucault's, but I hope I have correctly recalled the
essence of what he said. Or am I confusing him with some other source?

Does anyone recall reading something like this by Foucault (or some other
writer)?

Thanks in advance,
Nate

--
Nathaniel Roberts
Adjunct Assistant Professor
Department of Anthropology
Columbia University